一、基本元素

BeautifulSoup库是解析、遍历、维护“标签树”的功能库。

引用

 from bs4 import BeautifulSoup

 import bs4

html文档-标签树-BeautifulSoup类

 from bs4 import BeautifulSoup

 soup1 = BeautifulSoup(“<html>data</html>”,”html.parser”)

 soup2 = BeautifulSoup(open(“D://demo.html”),”html.parser”)

※一个BeautifulSoup对象对应一个HTML/XML文档的全部内容

 1 import requests
 2 from bs4 import BeautifulSoup

 r = requests.get("http://python123.io/ws/demo.html")

 r.text

 '<html><head><title>This is a python demo page</title></head>\r\n<body>\r\n<p class="title"><b>The demo python introduces several python courses.</b></p>\r\n<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n<a href="http://www.icourse163.org/course/BIT-268001" class="py1" id="link1">Basic Python</a> and <a href="http://www.icourse163.org/course/BIT-1001870001" class="py2" id="link2">Advanced Python</a>.</p>\r\n</body></html>'

 demo = r.text

 soup = BeautifulSoup(demo,"html.parser")

 print(soup.prettify())

 <html>

  <head>

   <title>

    This is a python demo page

   </title>

  </head>

  <body>

   <p class="title">

    <b>

     The demo python introduces several python courses.

    </b>

   </p>

   <p class="course">

    Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:

    <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">

     Basic Python

    </a>

    and

    <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">

     Advanced Python

    </a>

30    .

   </p>

  </body>

 </html>

在上述代码中，一个BeautifulSoup对象对应一个HTML文档的全部内容，可查看r，demo，soup的类型

 type(r)

 <class 'requests.models.Response'>

 type(demo)

 <class 'str'>

 type(soup)

 <class 'bs4.BeautifulSoup'>

BeautifulSoup库解析器

解析器	使用方法	条件
bs4的HTML解析器	BeautifulSoup(mk,’html.parser’)	安装bs4库
lxml的HTML解析器	BeautifulSoup(mk,’lxml’)	安装lxml库
lxml的XML解析器	BeautifulSoup(mk,’xml’)	安装lxml库
html5lib的解析器	BeautifulSoup(mk,’ html5lib’)	安装html5lib库

BeautifulSoup类基本元素

基本元素	说明
Tag	标签，最基本的信息组织单元，分别用<>和</>标明开头和结尾
Name	标签的名字，<p>…</p>的名字是’p’，格式：<tag>.name
Attributes	标签的属性，字典组织形式，格式：<tag>.attrs
NavigableString	标签内非属性字符串，<>…</>中字符串，格式：<tag>.string
Comment	标签内字符串的注释部分，一种特殊的Comment类型

以"http://python123.io/ws/demo.html"html文档为例，先生成soup对象（BeautifulSoup类），该文档的详细内容在※代码中可看到。

1 import requests
2 from bs4 import BeautifulSoup

 r = requests.get("http://python123.io/ws/demo.html")

 demo = r.text

 soup = BeautifulSoup(demo,"html.parser")

1、soup的标题及标签

文档中有两个a标签，直接使用soup.a只可以获得第一个a标签

 soup.title #标题

 <title>This is a python demo page</title>

 tag = soup.a #标签a

 tag

 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>

2、标签名

 soup.a.name #标签a的标签名

 'a'

 soup.a.parent.name #标签a的父标签名

 'p'

 soup.a.parent.parent.name #标签a的父标签的父标签名

 'body'

3、标签属性

 tag = soup.a #tag为soup中的a标签

 tag.attrs #标签属性值

 {'href': 'http://www.icourse163.org/course/BIT-268001', 'class': ['py1'], 'id': 'link1'}

 tag.attrs['class'] #标签'class'属性值

 ['py1']

 tag.attrs['href'] #标签'href'属性值

 'http://www.icourse163.org/course/BIT-268001'

 type(tag.attrs) #标签属性类型

 <class 'dict'>

 type(tag) #标签类型

 <class 'bs4.element.Tag'>

4、标签内非属性字符串

NavigableString可跨越多个层次，如下代码中p标签内还有b标签，但不会打印b标签，而是打印b标签内的字符串

 soup.a #标签a

 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>

 soup.a.string #标签a内非属性字符串

 'Basic Python'

 soup.p #标签p

 <p class="title"><b>The demo python introduces several python courses.</b></p>

 soup.p.string #标签p内非属性字符串

 'The demo python introduces several python courses.'

 type(soup.a.string) #标签a内非属性字符串类型

 <class 'bs4.element.NavigableString'>

 type(soup.p.string) #标签p内非属性字符串类型

 <class 'bs4.element.NavigableString'>

5、标签内字符串的注释部分

使用<tag>.string时显示的字符串类型可能是NavigableString，也可能是Comment。

 newsoup = BeautifulSoup("<b><!-- This is a comment --></b><p>This is not a comment</p>","html.parser") #创建一个新的BeautifulSoup对象

 newsoup.b.string #标签b的字符串

 ' This is a comment '

 newsoup.p.string #标签p的字符串

 'This is not a comment'

 type(newsoup.b.string) #标签b的字符串类型

 <class 'bs4.element.Comment'>

 type(newsoup.p.string) #标签p的字符串类型

 <class 'bs4.element.NavigableString'>

综上所述

<p class = "title">...</p>

标签 .<tag>

名称 .name

属性 .attrs

非属性字符串/注释 .string

二、HTML内容的遍历方法

1、标签树的下行遍历

属性	说明
.contents	子节点的列表，将<tag>所有儿子节点存入列表
.children	子节点的迭代类型，与.contents类似，用于循环遍历儿子节点
.descendants	子孙节点的迭代类型，包含所有子孙节点，用于循环遍历

以※处的html文档为例

 import requests

 from bs4 import BeautifulSoup

 r = requests.get("http://python123.io/ws/demo.html")

 demo = r.text

 soup = BeautifulSoup(demo,"html.parser")

head标签、head标签儿子节点及body标签儿子节点

 soup.head #head标签

 <head><title>This is a python demo page</title></head>

 soup.head.contents #head标签儿子节点

 [<title>This is a python demo page</title>]

 soup.body.contents #body标签儿子节点

 ['\n', <p class="title"><b>The demo python introduces several python courses.</b></p>, '\n', <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:

 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>, '\n']

 len(soup.body.contents) #body标签儿子节点数量

 5

 soup.body.contents[1] #body标签中的第二个儿子标签

 <p class="title"><b>The demo python introduces several python courses.</b></p>

综上

遍历儿子节点

 for child in soup.body.children:

     print(child)

遍历子孙节点

for descendant in soup.body.descendants

    print(child)

2、标签树的上行遍历

属性	说明
.parent	节点的父亲标签
.parents	节点先辈标签的迭代类型，用于循环遍历先辈节点

同样的，以※处的html文档为例

 soup.title.parent #title的父标签

 <head><title>This is a python demo page</title></head>

 soup.html.parent #html的父标签

 <html><head><title>This is a python demo page</title></head>

 <body>

 <p class="title"><b>The demo python introduces several python courses.</b></p>

 <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:

 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>

 </body></html>

 soup.parent #soup的父标签

由以上代码可知，title标签的父标签为head标签，html标签是html文档的最高级标签，其父标签就是自己。soup是一种特殊的标签，其父标签为空。

标签树的上行遍历

 soup = BeautifulSoup(demo,"html.parser")

 for parent in soup.a.parents:

     if parent is None:

         print(parent)

     else:

         print(parent.name)

3、标签树的平行遍历

平行遍历发生在同一个父节点下的各节点间

属性	说明
.next_sibling	返回按照HTML文本顺序的下一个平行节点标签
.previous_sibling	返回按照HTML文本顺序的上一个平行节点标签
.next_siblings	迭代类型，返回按照HTML文本顺序的后续所有平行节点标签
.previous_siblings	迭代类型，返回按照HTML文本顺序的前续所有平行节点标签

同样的，以※处的html文档为例

 soup.a.next_sibling #标签a的后续平行节点

 ' and '

 soup.a.next_sibling.next_sibling #标签a后续平行节点的后续平行节点

 <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>

 soup.a.previous_sibling #标签a的前续平行节点

 'Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n'

 soup.a.previous_sibling.previous_sibling #标签a前续平行节点的前续平行节点（为空）

 soup.a.parent #标签a的父亲节点

 <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:

 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>

遍历后续节点

 for sibling in soup.a.next_siblings:

     print(sibling)

遍历前续节点

 for sibling in soup.a.previous_siblings:

     print(sibling)

三、HTML的格式化和编码

prettify()方法